Thick film palladium-silver compositions are used in the manufacture of resistor or conductor elements, which have a variety of applications. Exemplary applications include the dissipation of the secondary voltage surge that occurs when lightning hits telecommunication wires; the sensing of changes in electrical current in circuits, where changes in current flow can be utilized to switch circuits or determine battery charge in portable electronics; electrically conductive termination for ruthenium based thick film resistors; and low temperature heating elements.
In a majority of such applications, low resistivity, below 1000 milliohms per square, is needed for good conduction of electrical current. For small, efficient circuits, a resistivity below 100 milliohms per square is needed. In addition, a low temperature coefficient of resistance (TCR), usually below 100 ppm/.degree.C., is required to keep the resistance constant over a given temperature range. The lower limit of the temperature range is traditionally defined as -55.degree. C. or -40.degree. C., the ambient temperature encountered in cold regions of the earth. The upper temperature limit is traditionally defined as +125.degree. C., a temperature that the entire assembled circuit is likely to encounter either due to heat generation by the circuit itself or by proximity to a heat source, such as in an under-the-hood automotive application.
It is known that low TCR can be achieved for thick film compositions by selecting a particular weight ratio of palladium to silver components in the composition, typically in the range of about 56/44 to about 60/40. The ordinary glass binder systems used in these thick film compositions typically comprise, in a major portion, SiO.sub.2, PbO, and Al.sub.2 O.sub.3, and in a minor portion, CaO, B.sub.2 O.sub.3, Na.sub.2 O, K.sub.2 O, and MgO. Within this Pd/Ag ratio range, and using ordinary glass binder systems used in thick film compositions, sheet resistivities in excess of 100 milliohms per square generally result.